Page drag-n-drop : Frontend part (1/2)

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Page drag-n-drop: Backend support for moving pages inside a same document (1.5/2)

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Page drag-n-drop: Backend support for moving pages from a document to another one (2/2)

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Work directory: Default permissions should be 0750, not 0755

Signed-off-by: Jerome Flesch <jflesch@gmail.com>